About Converters
Half the world measures one way and half the other, so conversions turn up in recipes, luggage allowances, road signs, clothing sizes, medical records and spec sheets. Most of these ratios are exact by international agreement rather than approximate: an inch is precisely 2.54 centimetres, a pound is precisely 0.45359237 kilograms, and a mile is precisely 1.609344 kilometres.
Each converter here works in both directions at once — type into either box and the other follows — and shows the alternative units people usually want alongside. Weight includes stones and ounces, length includes feet and inches for height, and distance doubles as a speed converter because km/h and mph share the same ratio.
Temperature is the odd one out: Celsius and Fahrenheit have different zero points as well as different step sizes, so the conversion is a multiplication followed by an addition rather than a single ratio. That is also why −40 is the one temperature where both scales agree.